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Old 06-12-2008, 02:24 PM   #61
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Originally Posted by Rayme View Post
The turbocharged Mazdaspeed3 uses direct injection, and so is the new turbocharged Ecotec in the Cobalt...and GM is going to introduce another..turbocharged! Small engine in the future (sub 2.0). It does make the fuel burn better, to can get away with better MPG and Emission !

Now I don't know how exactly direct injection works, (does it gets injected right before the sparks, or while the intake valves open?), so I don't know how good it is at detering knock, I didn't read much on the subject to be fair.

The best way to control detonation is simple (like in diesel), just inject the fuel when it's supposed to burn(direct injection)

Diesel is like 170 ron? something high like that right?

I am not sure petrol would work with direct injection or else they or somebody would have done it by now? is that fair to say?

You know maybe Smokey Vapour engine used some kind of detonation instead of burn? I think there is more power in the detonation then in the burn process.

Don't be trying to confuse him with facts or anything.
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Old 06-12-2008, 05:48 PM   #62
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very clear writing- good info, thanks.

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The compression of an engine without ignition is from 120-200psi depending upon the compression ratio of the engine. The ignition of fuel produces a burn time of many degrees in fact my xB timing is advanced as much as 38 degrees BTDC under light loads and I am sure that it continues to burn as the piston is moving downwards or else they would not ignite it so soon because they would want the peak pressure to occure after TDC or else the engine would want to run backwards. That is an example of slow burning. Under heavy loads the timing is retarded to just a few degrees BTDC (Before Top Dead Center) and since the piston is confining the gasses to such a small volume it can burn more quickly (less distance for the flame to travel) with less of the heat energy being absorbed by the engine cylinder walls because less of the walls are exposed to the flame because the piston is covering it almost completely - actually a few degrees BTDC the piston is essentially all the way up in its travel. Now you have all the air and fuel charge compressed into a small space and then ignition occurs further increasing the pressure even more. But because it burns somewhat slowly (in terms of crank rotation) the piston is moving downwards reducting the pressure as it is rising from the thermal expansion and production of gasses from the complex hydrocarbon fuel breakdown from combustion. This produces a smooth increase in pressure and transfer of energy to the crank. If fuel ignited really quickly there would be no need for timing changes / advancing.
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Old 06-12-2008, 06:21 PM   #63
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I did a mild port job and match job on a d16y5 (hx) and bumped the compression to 10.3 to 1 but left the cam and ecu stock. I have it running pretty well but I am still iorning out the bugs. I advanced the cam timing 3 degrees- it helps the 12 valve mode out quite a bit. I'll put the project up here soon and share documentation.

Oh and I thought bowie was cool as Tesla in that magician movie.

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I would say the best head you have with the stock cam if that combination is possible would probably get you the best mileage, turbo or not. Improved head efficency as long as it isn't only for high rpm use by enlarging the ports excessively can help mileage out I would say. Any time you make the air flow through the head smoother that has to help the engine get better mileage. Just don't enlarge the ports so that it has bad flow velocity at low rpms where you are trying to get better mileage.

Also higher compression can help but don't make it run on race gas only or you won't really be saving money

I haven't really tried any major changes to an engine to get better mileage so I could be off on what I say.
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Old 06-12-2008, 06:29 PM   #64
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mimi-e. Retard your spark timing 3 degrees.
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Old 06-12-2008, 08:59 PM   #65
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Lotsa good, relevent info here about knock.
http://www.max-boost.co.uk/max-boost...ion_deeper.htm
In short, knock is bad because it raises the peak pressure too early.

According to this site http://www.prime-mover.org/Engines/G...es/octane.html
"Diesel and Jet fuel (along with kerosene) have, indeed, terrible octane numbers; typically about 15-25 "octane". They tend to ignite easily from high compression. Their use in a gasoline engine will quickly destroy the engine."
This makes sense to me since a diesel relies on the fuel igniting itself, so the best fuel to use in a diesel is one that is easily self-ignited.
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Old 06-19-2008, 01:19 AM   #66
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All of you guys (or gals) should go and look up the workings of Diesel engines - they are COMPRESSION IGNITION engines and use NO spark to ignite the fuel air mixture. Air is compressed in the cylinder on the compression upstroke; it gets hot and then the fuel is injected before top dead centre. The fuel continues to burn as the piston descends on its power stroke, the point at which this ceases has a lot to do with whoever is controlling the engine's power output. So they commonly have pre-ignition, as it would be called on a spark ignition engine. It is called diesel rock, or knock, and does not make a pinging sound, rather a clatter easily heard over the sound of the exhaust. Diesel fuels are nor given an octane rating - it would be quite low, but they are given a cetane number "...a measure of a fuel's ignition delay; the time period between the start of injection and start of combustion (ignition) of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. Cetane numbers are only used for the relatively light distillate diesel oils. For heavy (residual) fuel oil two other scales are used CCAI and CII." Go look it up!
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Old 06-19-2008, 01:31 AM   #67
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Oh, dear, I seem to have just posted to the October 2006 portion of this thread, and so what I've just posted my have been covered earlier. Second thoughts after looking back over the complete thread indicate that my post had not been previously covered, I'd just missed the bit concentrating on the intricacies of electrical sparks igniting the fuel, but let me throw in another quote (reputable source) "...octane rating does not relate to the energy content of the fuel, nor the speed at which the flame initiated by the spark plug propagates across the cylinder. It is only a measure of the fuel's resistance to autoignition" The term "auto-ignition" can probably be taken for compression ignition. Has anyone recently tried igniting a petrol or gasoline/air mixture with a spark struck from a flint by a steel? Worth thinking about.
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Old 06-19-2008, 09:03 AM   #68
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Originally Posted by richochet View Post
.octane rating does not relate to the energy content of the fuel, nor the speed at which the flame initiated by the spark plug propagates across the cylinder.
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Diesel has an octane number of about 15-25. The reason for this seemingly terrible number compared to the ones we're used to from gasoline is the fact that diesel is combusted in a totally different type of engine. Diesel has low volatility, low knock resistance, yet high energy per volume. Because of its low knock resistance, diesel should not be used in a gasoline engine as it will destroy it very quickly and efficiently.
I guess Diesel can not produce the same kind of knock or ping as a petrol engine.
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Old 06-19-2008, 09:42 AM   #69
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It also has to do with the air/gas mix being compressed together in a standard gasoline engine and therefore they could self ignite at 50 degrees BTC if there was a hot spot or if the engine was overheated.

But, in a diesel, only the air is compressed. The diesel is injected into the cylinder immediately before its supposed to ignite. So, unless the timing of your diesel injection pump was wayyyyy off, there is no way that you could ever get an ignition event at 50 degrees BTC because there normally isn't any diesel in the cylinder to burn at that time.
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Old 06-19-2008, 09:51 AM   #70
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I guess Diesel can not produce the same kind of knock or ping as a petrol engine.
No pinging, but the principle behind knocking is why a diesel works. Techincally if a diesel isn't knocking its not running.

-Jay
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